1. Technical Field
The present invention relates to light guide plates that are a component of edge-light-type surface light source equipment useful as the back lights of rear projection liquid crystal displays, sign boards, and the like; to a process for producing the same; and to surface light source equipment and liquid crystal displays that utilize the same. Particularly, an object of the present invention is to provide light guide plates having high efficiency for light utilization, with which back lights can be made thin, and surface light source equipment and light crystal displays that use such light guide plates.
2. Background Art
Conventional back lights for use in rear projection displays such as liquid crystal displays are classified into edge type and direct type, depending upon the position of their light sources. However, in the case of liquid crystal displays, mainly used are edge-light-type back lights with which thinner liquid crystal displays good for space savings can be obtained.
FIG. 5 is a cross-sectional view showing one example of an edge-type, single-light-type surface light source equipment.
As shown in FIG. 5, such a surface light source equipment is composed of a light guide plate 1, a linear light source 2, a light-reflecting film 3, a light-diffusing film 4, a lens film 5, and the like. For the linear light source 2, a cold cathode tube is used; and a metal-deposited resin film or the like is used for the light-reflecting film 3. Further, in order to correct that the quantity of emergent light from the light guide plate decreases as the distance from the light source becomes great, a light-emerging pattern 11 composed of white dots is formed, by means of printing, directly on the back surface of the light guide plate, or on the light-reflecting film 3 to be provided on the back surface of the light guide plate, in such a manner that the dots become dense as the distance from the light source becomes great. Since this light-emerging pattern is so formed that the density of the dots becomes high as the distance from the light source becomes great (on the right side in the figure), the quantity of emergent light at the side fare from the light source is prevented from becoming insufficient. The light-diffusing film 4 scatters emergent light from the light guide plate, and prevents the light source and the dots of the light-emerging pattern from being directly seen by light. In addition, this film broadens light to increase the viewing angle of a display. Further, for the lens film 5, a resin film on which a large number of, for example, triangular or semi-ellipsoidal prisms are two-dimensionally arranged, or the like is used.
In such a surface light source equipment, it is demanded to make the light guide plate thin in order to meet the need for thinner, light-weighted liquid crystal displays, etc.
There has been effected, as a method for producing conventional light guide plates, (1) a method in which an acrylic plate is cut and polished, or (2) a method using injection molding. However, the method (1) is complicated in production process, and desired shapes cannot be obtained by this method. Further, although the method (2) is advantageous in that desired shapes can freely be obtained, it is impossible to obtain, by this method, thin molded products with thicknesses of 1 mm or less due to the limit of the flowability of resins.
Accordingly, a primary object of the present invention is to provide a light guide plate whose maximum thickness is 1.0 mm or less, and a simple process for producing such a light guide plate.
Thus, the present invention provides a light guide plate for use in the surface light source equipment of a liquid crystal display or the like, wherein the light guide plate is a molded product of an ionizing-radiation-curable resin, and its maximum thickness on the light-source-fixing part side is 1.0 mm or less.
According to an embodiment of the present invention, a light-diffusive film is integrally formed on the above-described light guide plate on its light-emerging surface side.
According to another embodiment of the present invention, a lens film is integrally formed on the above-described light guide plate on its light-emerging surface side.
The present invention also provides a process for producing a light guide plate, comprising the resin-coating step of forming a resin mass of an ionizing-radiation-curable resin at one end of the inside of a mold for shaping a light guide plate; the step of placing an ionizing-radiation-transmissive film on the resin mass of the ionizing-radiation-curable resin; the step of spreading the film on the ionizing-radiation-curable resin while filling the mold with the ionizing-radiation-curable resin through the film by the use of press rolls; the step of curing the ionizing-radiation-curable resin by applying thereto ionizing radiation; and the step of releasing the molded product of the ionizing-radiation-curable resin from the mold.
In the above process, the ionizing-radiation-transmissive film may be a light-diffusive film, or a film in the shape of a lens.
Further, the above-described process may further comprise the step of separating the film from the molded product released.
According to the present invention, extremely thin light guide plates whose maximum thicknesses are 1.0 mm or less, such small thicknesses being unattainable by any of conventional processes, can accurately be formed in any shape as desired. By the use of such light guide plates, it is possible to obtain thin, light-weighted surface light source equipment and liquid crystal displays.